New Boiler (Worcester Bosch Greenstar 4000)

FreeBear

frostysaver said:

tux900 said:

A visible plume is actually a *good* sign. Steam (water >100C) is invisible, so what you are seeing is water vapour resulting from a condensing boiler recovering some of the latent heat of the exhaust gases which cools them down to <100C hence becoming visible. 

This is kinda but not completely correct.

Some heat is recovered cooling hot gases and water vapour a bit, which would make a more visible cloud plume.

However much more heat is extracted by condensing the water vapour to liquid water, which runs down a drain. In that case there won't be a big visible cloud plume.
This is the "latent heat" to change water phase gas->liquid.

Bearing in mind @tux900 made that comment back in 2021, I would go as far as to say it is completely incorrect for a modern condensing boiler Condensing only takes place below ~54°C where boiler efficiency starts to increase - The lower the exhaust temperature, the better, and this can be gauged to some extent by the amount of visible plume.

Modern flue systems often use plastic to contain the exhaust fumes - They are typically rated for 80°C max, so if your exhaust fumes are hitting 100°C or more, there is a problem with the boiler.

@MigsyBigsy - The best temperature to run your central heating at depends on how big your radiators are and how fast you want to heat the house to. If I set my flow temperature to 60°C, my house takes about 2 hours to warm up by 3°C. Turn the flow temperature down to 45°C, and it takes twice as long and doesn't really use any less gas. I'd suggest playing around with the flow temperatures and find a setting that suits you. But the lower you can go, the boiler will be pushed further in to condensing mode.

With a combi boiler, there is no real need to set the hot water temperature any higher than you need - I have mine set to ~45°C which is just right for a bath. If you have a hot water tank, some will advise that 60°C is the minimum to avoid Legionella. But with only some 400 cases reported each year, you have a better chance of being run over by a No.13 bus. With a hot water tank, anything over 50°C is enough to kill bacteria (just takes a few hours rather than minutes).

Lorian

In my experience you usually see a noticeable plume even when a boiler is in the sweet spot for condensing when it's about -4c to +2c outside.

QrizB

Lorian said:

In my experience you usually see a noticeable plume even when a boiler is in the sweet spot for condensing when it's about -4c to +2c outside.

The plume from a properly condensing boiler will be thin and wispy. One that isn't condensing properly will have a much thicker and persistent plume. Or at least that's my experience.

FreeBear

QrizB said:

Lorian said:

In my experience you usually see a noticeable plume even when a boiler is in the sweet spot for condensing when it's about -4c to +2c outside.

The plume from a properly condensing boiler will be thin and wispy. One that isn't condensing properly will have a much thicker and persistent plume. Or at least that's my experience.

Was down to -4°C here, and is only now creeping up to 0°C. Looking at my flue, you'd be hard pushed to see any plume. But I've got my exhaust temperature down to under 50°C, so well in to condensing mode.

gazb_2

I have my worcesterbosch 8000 system boilers flow temperature set at 60, how do I know what the dryer or exhaust temperature is?

FreeBear

Some boilers, you can query various internal sensors with an app or with custom hardware - I'm using a DIY interface to talk to my Viessmann boiler via the OpenTherm interface. WB has a similar type of (incompatible) interface called EMS. There are similar DIY hardware projects that you can use, for example, EMS-ESP.

Most (all ?) modern boilers also have an access port where the flue exits the boiler. It is possible to insert a thermometer in this hole, but I wouldn't recommend it. Carbon Monoxide (that is CO, no 2) and NOX will escape in to the building.

A safer method would be to clip a pipe termometer on to the return - Your exhaust temperature will be around 5°C higher. But don't get hung up on temperatures. As long as the plume coming out of the exhaust terminal is light and wispy, you are getting good efficiency.

Lorian

Or a temp probe on return pipe, or an infrared camera. I use a cheap probe/data logger on the return.

tux900

Lorian said:

Or a temp probe on return pipe, or an infrared camera. I use a cheap probe/data logger on the return.

Yeah I do similar with a Shelly Uni and a couple of 1-wire temperature probes strapped to the flow and return.

FreeBear

tux900 said:

Lorian said:

Or a temp probe on return pipe, or an infrared camera. I use a cheap probe/data logger on the return.

Yeah I do similar with a Shelly Uni and a couple of 1-wire temperature probes strapped to the flow and return.

Found most (all ?) of those DS18b20 sensors to be inaccurate and non-linear. Fortunately, esphome has curve fitting algorithms that reduce the errors.

It would appear that you are cycling your boiler quite a bit during the day - That is going to have an impact on your overall efficiency. If you can "do" modulation, well worth investing in the hardware. As a bonus, you get even more data to log

For giggles, a few hours of data from my heating this morning.

tux900

FreeBear said:

Found most (all ?) of those DS18b20 sensors to be inaccurate and non-linear. Fortunately, esphome has curve fitting algorithms that reduce the errors.

Might they have been fakes? It seems there's an awful lot of them about. I reckon the vast majority in fact given the ubiquity of sellers on the likes of eBay and Amazon etc with completely unknown supply chains. It's a race to the bottom. I prefer to use the likes of RS and CPC etc for things like this; sure you do pay more but at least you can be confident you are getting the real deal.

It would appear that you are cycling your boiler quite a bit during the day - That is going to have an impact on your overall efficiency. If you can "do" modulation, well worth investing in the hardware. As a bonus, you get even more data to log

The cycling is just down to Honeywell's TPI control algorithm. Rather than wait for the sensed temperature to fall below (or rise above) the set threshold it periodically calls for heat to maintain tight control over the output with little if any hysteresis. It works extremely well with hardly any ripple at all. An often-assumed downside is that it increases wear on the system but I've been running this for 14 years now with no failures (literally zero in repairs cost over the entire time) so the concern is massively overblown in my experience. I would still prefer to have analogue modulation control though as, like you say, it could only improve efficiency even further however it is not an option with our boiler (a relatively simple 15KW Ideal Icos, which can only modulate itself down to 9KW which is way higher than we need) and our heating costs are pretty reasonable despite the heating being on all day every day so there's little motivation to replace it just yet. I doubt any replacement could pay for itself in its lifetime in terms of efficiency savings over the purchase and installation cost.